The use of rootstocks in grape production is often necessary in California due to soil pests such as nematodes and soil problems. Nematodes are microscopic roundworms that feed on and damage plant roots reducing vine vigor and production. Of the many nematodes in the state, root knot (Meloidogyne spp.), dagger (Xiphinema americanum and index), ring (Mesocriconema xenoplax) and root lesion (Pratylenchus vulnus) are of most concern.

Root knot nematodes penetrate the roots of vines and cause swellings, or galls, which disrupt root function. The dagger nematode feeds near the root tips and may cause damage but is more importantly a vector of grapevine fanleaf and yellow vein viruses. Pre-plant soil fumigation and the use of rootstocks are regarded as the best defense against plant parasitic nematodes.

No single rootstock offers resistance to all nematodes. However, recent breeding efforts have focused on providing durable and broad resistance to aggressive nematode populations. An example of this effort is the release of two new grape rootstocks varieties bred by David Ramming, USDA-Fresno and selected by Michael McKenry, UC Riverside Nematology Department last fall. The new varieties, RS-3 and RS-9, are hybridized Ramsey and Schwarzmann rootstocks which offer broad resistance to nematodes and should be available during the fall of 2004.

RS-3 is a moderately vigorous rootstock that is suitable for coarse to fine sandy loam soils. Resistance is available to all known aggressive pathotypes of root knot nematode and offers moderate resistance to X. index, resistance to root lesion nematode and tolerance to grapevine fanleaf virus. In contrast, RS-9 is a low vigor rootstock, equivalent to Schwarzmann or 101-14. It is suitable for evaluation in high density situations and should be considered primarily for coastal valleys and coarse-textured soils. Like RS-3, RS-9 is resistant to all aggressive of root knot nematode and exhibits good resistance to X. index and root lesion nematode.

If you are interested in ordering RS-3 or RS-9 rootstock please contact Foundation Plant Services at UC Davis, (530) 752-3590 and Bill Tucker, UC Office of Technology Transfer Licensing Officer, (510) 587-6000.